1. Field of the Invention
The present invention relates to a variable drive current driver circuit.
2. Description of the Prior Art
According to the conventional standards, such as IEEE 1394 standards, a drive current of a signal transmitted between electronic devices, such as personal computers, video movies, or mini-disc players, connected mutually via a cable or the like is determined so as to become either of two kinds. When a certain electronic device is connected to another electronic device via a cable, the former have the latter notify the former of the standard of a signal that can be received by the latter, and the former transmits data with a drive current determined on the basis of this notification.
FIG. 1 is a diagram showing a conventional driver circuit that is capable of varying a drive current of a signal. In the conventional technique, as shown in FIG. 1, a driver circuit for either a standard A or a standard B is driven on the basis of, for example, a control signal of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d so as to be able to cope where the electronic device of the opposite party receives a signal of either of the two kinds of drive current defined by the standard.
In other words, if a control signal of xe2x80x9c1xe2x80x9d is inputted to the standard A driver circuit and the standard B driver circuit, then the standard A driver circuit is enabled and the standard B driver circuit is disabled. If a control signal of xe2x80x9c0xe2x80x9d is inputted to the standard A driver circuit and the standard B driver circuit, then the standard A driver circuit is disabled and the standard B driver circuit is enabled.
In the conventional technique, however, it is necessary to prepare as many driver circuits as the number of kinds of the driver current defined by the standard. As a result, the circuit scale becomes large as the number of kinds of the drive current increases, especially in an electronic device, where transmission and reception of a plurality of data are performed using one physical layer LSI, it is especially desired to prevent the circuit scale from becoming large.
Therefore, the object of the present invention is to provide a variable drive current driver circuit having a small scale.
According to the first aspect of the present invention, there is provided a variable drive current driver circuit, comprising: a pair of push-pull circuits for driving a load circuit complementarily; a first current source circuit for having a bias current flow into the pair of push-pull circuits; and a control circuit for varying both the bias current flowed by the first current source circuit and the bias current flowed by the second current source circuit according to a control signal.
In the variable drive current driver circuit, the first current source circuit comprises a current mirror circuit, and the control circuit controls an input current of the current mirror circuit according to the control signal.
In the variable drive current driver circuit, the control circuit may control the input current by controlling a control terminal voltage of a transistor for flowing the input current.
In the variable drive current driver circuit, the control of the control terminal voltage may be performed by changing, by a transistor which turns on or off according to the control signal, a magnitude of a load which flows through the output.
In the variable drive current driver circuit, the second current source circuit may comprise a transistor, and the control circuit may control a control terminal voltage of the transistor according to the control signal.
In the variable drive current driver circuit, the control of the second current source circuit may be performed by changing, by a transistor which turns on or off according to the control signal, a magnitude of a load which flows through the output.
According to a second aspect of the present invention, there is provided a variable drive current driver circuit, comprising: a pair of push-pull circuits for driving a load circuit complementarily; a first current source circuit for having a first bias current flow into the pair of push-pull circuits; a second current source circuit for having the first bias current flow out of the pair of push-pull circuits; a third current source circuit capable of having a second bias current flow into the pair of push-pull circuits; a fourth current source circuit capable of having the second bias current flow out of the pair of push-pull circuits; and a control circuit for varying both the second bias current flowed by the third current source circuit and the second bias current flowed by the fourth current source circuit according to a control signal.
In the variable drive current driver circuit, the control circuit may have the third current source circuit have the second bias current flow nor not flow into the pair of push-pull circuit, and the control circuit may have the fourth current source circuit have the second bias current flow or not flow out of the push-pull circuit.